1. Field of the Invention
The present invention relates to an object detection system, and more specifically, relates to an object detection system, a drive assist system provided with the object detection system, and an object detection method that detect vehicles, obstacles and the like on a road.
2. Description of the Related Art
Drive assist systems that detect a distance and a relative speed between a host vehicle and a preceding vehicle, and control throttles and brakes to automatically keep the speed and the following distance of the host vehicle at set values, have been put to practical use. In the field of such drive assist systems, as technologies for detecting objects such as vehicles in the path of the host vehicle, radar systems using millimeter radio waves or the like are available. In Japanese Patent Application Publication No. 2004-191131 (JP-A-2004-191131), a technology is described in which a higher threshold value for identifying vehicles and a lower threshold value for identifying pedestrians are set, and an object is identified as a vehicle when the intensity of a received radio wave is equal to or higher than the higher threshold value, and an object is identified as a pedestrian when the intensity of a received radio wave is equal to or higher than the lower threshold value.
However, with regard to the above technology, the higher threshold value is set in order to identify vehicles, which can cause a problem that objects, such as motorbikes and bicycles, from which a radio wave of low intensity is received, can be easily and frequently lost even after the object is detected. When a drive assist system that causes the host vehicle to follow a preceding vehicle frequently loses an object, the drive assist system repeatedly determines that a preceding vehicle is present, and that no preceding vehicle is present, within a short time, so that the drive assist system causes the host vehicle to perform unnecessary acceleration and deceleration. On the other hand, when a lower threshold value is set for use in identifying vehicles, control is performed with respect to the ghost caused by road surface reflection, etc, and, as a result, erroneous control and erroneous warning can easily occur.